The long-term goal of the proposed research is to elucidate the molecular pathway regulating embryonic endoderm formation in vertebrates. The endoderm contributes to the respiratory and gastrointestinal systems and sends essential developmental signals to the head and heart mesoderm. Recent work in Xenopus, mouse and zebra fish has elucidated a conserved molecular pathway that initiates vertebrate endoderm specification during gastrulation. The transcription factor Sox17 is essential in this pathway but the downstream genetic cascade it regulates is poorly understood. Using a candidate gene approach the PIs have identified a number of Sox17 transcriptional targets in Xenopus, and orthologues of most of these are also expressed in the mouse endoderm. This observation has led them to hypothesize that the entire genetic pathway downstream of Sox17 is largely conserved between Xenopus and mouse. The specific aim of this proposal is to test this hypothesis and to identify the putative Sox17 target genes conserved between Xenopus and [unreadable] mammals. The PIs plan to couple established functional experiments in Xenopus with microarray analysis to identify targets of Sox17 in the frog. This data will be compared to the unique catalogue of genes expressed in the gastrula mouse endoderm, allowing them to identify candidate Sox17 target genes in the mouse and to determine the extent to which the genetic cascade downstream of Sox17 is conserved. The approach utilizes newly available Xenopus genomic resources in combination with existing mouse resources, in a type of analysis previously not possible. The results will facilitate future comparative studies that benefit from the complementary experimental advantages of these model systems. [unreadable] [unreadable]